This application relates generally to gas turbine engine rotor blades and, more particularly, to methods and apparatus for reducing vibrations induced to rotor blades.
Gas turbine engine rotor blades typically include airfoils having leading and trailing edges, a pressure side, and a suction side. The pressure and suction sides connect at the airfoil leading and trailing edges, and span radially between the airfoil root and the tip. An inner flowpath is defined at least partially by the airfoil root, and an outer flowpath is defined at least partially by a stationary casing. For example, at least some known compressors include a plurality of rows of rotor blades that extend radially outwardly from a disk or spool.
Known compressor rotor blades are cantilevered adjacent to the inner flowpath such that a root area of each blade is thicker than a tip area of the blades. More specifically, because the tip areas are thinner than the root areas, and because the tip areas are generally mechanically unrestrained, during operation wake pressure distributions may induce chordwise bending or other vibrational modes into the blade through the tip areas. Vibratory stresses, especially chordwise bending stresses (stripe modes), may be localized to the blade tip region. Over time, high stresses may cause tip cracking, corner loss, downstream damage, performance losses, reduced time on wing, and/or high warranty costs. Moreover, continued operation with chordwise bending or other vibration modes may limit the useful life of the blades.
To facilitate reducing tip vibration modes, and/or to reduce the effects of a resonance frequency present during engine operations, at least some known vanes are fabricated with thicker tip areas. However, increasing the blade thickness may adversely affect aerodynamic performance and/or induce additional radial loading into the rotor assembly. Accordingly, to facilitate reducing tip vibrations without inducing radial loading, at least some other known blades are fabricated with a shorter chordwise length in comparison to the above described known blades. However, reducing the chord length of the blade may also adversely affect aerodynamic performance of the blades.